1. Field of the Invention
This invention relates to safety apparatus for protecting the legs and lower torso of the occupant of a motor vehicle to reduce the extent and severity of injuries sustained during a crash. This invention more specifically relates to using an inflatable bolster to restrain the occupant""s legs and lower torso during a survivable crash.
2. Background of the Invention
During a frontal impact, the occupant moves forward due to the inertia and kinematics of the crash while the front components of the vehicle structure (bumper, hood, engine cavity) begin to collapse. Knee and leg injuries occur when the body of an occupant slides or submarines forward and/or downward and the occupant""s knees hit the instrument panel or structure beneath the panel. Further injuries occur when the occupant""s lower torso and legs move forward such that the knees are trapped in or beneath the instrument panel just before the foot well begins to collapse. As the foot well collapses, it pushes the occupant""s feet backward, causing the knees to elevate and become further trapped. As the foot well continues to crush, the loads on the trapped legs increase and cause foot, ankle, and tibia injuries. These injuries are common even with fixed knee bolsters designed to meet present knee injury criteria requirements.
Abdominal and lower torso injuries can be inflicted by the lap and lower part of the torso belts as they ride upward on the soft tissue of the occupant""s torso when he slides forward and downward due to the forces of the frontal crash.
The present invention, inflatable tubular bolster (ITB), protects the knees, femurs and lower torso as well as the feet, ankles, and lower legs of the occupant by creating an inflatable restraint that deploys in front of the occupant""s knees and inhibits forward and downward movement by the occupant during a frontal crash. It protects by preventing the knees from becoming trapped in or underneath the dashboard. Further, by transferring energy from the lower torso of the occupant through the femur and knees to the invention itself, this invention reduces the severity of injuries to those body parts as well. This invention also reduces the severity of lower torso injuries due to seat belt pressure by stabilizing the lower body and preventing the knees and legs from moving forward, thus allowing the seat belt to remain in its preferred position on the occupant.
The present invention improves egress and extraction of the occupant from a vehicle after a crash because it prevents the occupant from becoming wedged into or underneath the interior structure. Since this invention is smaller in size prior to being deployed, similar to an air bag, it does not intrude into or occupy significant space within the occupant compartment as does a conventional fixed knee bolster. This is a major advantage from not only the entry, egress and overall comfort viewpoints, but also from an aesthetic design consideration.
This invention is installed beneath or as part of the lower face of the dashboard. One end is rigidly attached to the vehicle side structure near the door while the other end is attached either to the center tunnel for single occupant use or to the other side of the vehicle for multiple occupant use. In the stowed position, the tube is flat and hidden from the occupant""s line of sight. This invention is stowed around the upper perimeter of the leg space behind a piece of trim or under a split-seam in the dashboard face. Original equipment manufacturers will be able to install the system into current platforms and integrate the device into future platforms.
The gas generator which inflates the unit can be mounted remotely in a convenient location, such as forward in the dashboard using a flexible or combination rigid/flexible gas conduit to this invention.
In the event of a crash, a crash sensor signals the gas generator to ignite and discharge gas at a high mass flow rate into the gas conduit leading to the ITB. As the ITB inflates, its length significantly decreases as its diameter increases. The ITB becomes semi-rigid as inflation completes, and it pulls itself out of its stowed position downward and rearward into its functional position. Within about 12 to 25 ms after impact, the taut, tubular cushion positions itself in front of the occupant""s knees, restrains forward and downward occupant movement, cushions the occupant from impact, and functions as a barrier between the occupant""s knees and legs and the vehicle""s structure. When the occupant hits the ITB, impact forces are transferred to the vehicle""s structure through this invention webbing and hardware. When the impact has passed and the occupant is at rest, he relaxes the load on this invention and is very close to his initial position.
Unlike conventional inflatable restraints, this invention uses an inflatable braided tube of continuous high-strength fiber, as described in U.S. Pat. No. 5,480,181, which is incorporated herein by reference. These fibers seek an orientation that accommodates a greater volume within the tube when under pressure. Prior to inflation, the fiber spirals are stretched-out longitudinally and the tubular restraint has a relatively small diameter. During inflation, the spirals move closer together longitudinally to increase the braided tube""s diameter and decrease its length, or contract.
The contraction in length of the braided tube during deployment and the consequently high tensile forces developed at its fixation points constitute a significant difference between the present invention and prior art. Uninflated, the orientation of the braided tube""s fibers are at a longitudinal angle of 30 degrees to 70 degrees to each other. Though the fibers theoretically seek a maximum longitudinal angle of 110 degrees during inflation, in actual tests the post-inflation orientation is typically 100 degrees in an unloaded, or unconstrained tube. The range of typical contraction of the unconstrained inflatable tube is 21.5 percent (for the 70 to 100 degree change) to about 33.5 percent (for the 30 to 100 degree change).
The calculation for determining the amount of contraction occurring upon inflation in an unconstrained condition for the present invention is as follows:
Lfxe2x88x92Li=X
where:
X is the amount of contraction
Lf is the length of flat, uninflated material
Li is the length of unconstrained inflated material, and
xcex8f is the longitudinal angle prior to inflation
xcex8i is the longitudinal angle after inflation and
Li/Lf=cos(xcex8i/2)/cos(xcex8f/2) hence
Lfxe2x88x92Li=Lf(1xe2x88x92(cos(xcex8i/2)/cos(xcex8f/2)))
For example, an embodiment of the present invention having an uninflated length of 100 cm and constructed with fibers that cross each other at a 36 degree angle would decrease in length, or contract, to 67 cm, approximately 33 percent, upon inflation in an unconstrained condition. (The calculation assumes that the angle of the fibers in an unconstrained inflated braided tube will be 100 degrees.)
The present invention contracts as a result of both inflation and contraction, typically contracting 21.5 percent to 33.5 percent from the change in orientation of the fibers (construction) plus an additional small percentage (Lfxe2x88x92Li=Df(1xe2x88x922/xcfx80)) as a result of the inflation pressure. Prior inventions, however, contract in length solely due to inflation, yielding a comparatively small contraction of approximately 7 to 10 percent. This greater contraction that this invention undergoes causes the restraint to be tighter and therefore develop high tensile forces at its fixation points. A tighter restraint is more resistant to deflection and allows more force to be directed through the webbing of this invention attachments to the vehicle structure. The occupant""s knees, legs, and lower torso will therefore move less, and thus the occupant is less likely to be injured.
Another important difference between this invention and prior art is that the present invention can be installed without any reactive surface behind the invention. Most prior art restraint devices of this type require the dashboard to extend low enough to provide a reactive surface for either the knees or a conventional air bag. This invention does not require this additional surface area protruding from the dashboard since it is supported by the high tensile forces developed at its fixation points. This invention therefore allows more leg room for the occupant in its un-inflated condition, increasing occupant comfort and reducing the possibility that the occupant will be trapped beneath the dashboard during a crash. Because prior art restraint devices need strong reactive surfaces, the total system (module and support structure) can be heavy and/or bulky. The present invention does not include nor require a heavy support structure since it employs the already existing vehicle side structure and/or tunnel.
Fixed bolsters cannot provide optimal protection for both small and large occupants because seat positions vary. A small occupant, for example, sitting in a rearward seat position, as commonly occurs on the passenger side, will come off the seat prior to contacting a fixed bolster. The occupants can thus be injured by hitting the rigid padding or structure of the bolster. Since the present invention is a non-rigid structure, fewer injuries would result from hitting the bolster itself, and it can position itself further rearward than a fixed bolster and thus xe2x80x9ccatchxe2x80x9d the small occupant""s knees before the occupant comes off the seat. This invention deploys only in response to a crash sensor signal and thus does not hinder occupant movement and comfort when it is not needed for protection.
Lastly, the present invention may be inflated to a range of diameters depending on the particular vehicle installation. The typical inflation diameter is approximately 200 mm. This allows this invention a larger surface area for distribution of forces and occupant restraint than fixed knee bolsters. This large diameter fills the space in front of the occupant""s legs very quickly and immediately provides a cushioned barrier that protects the lower torso, knees, and legs.
The present invention, therefore, is an important contribution to vehicular crashworthiness and occupant leg and torso protection in frontal impacts and is particularly a substantial improvement in inflatable vehicular knee bolsters.